Digit adding selector



Sept. 30, 1958 w. w. PHARIS I 2,854,518

DIGIT ADDING SELECTOR Filed March so, 1956' s Sheets-Sheet 2 H2- TO INT. CCT.

TPI

FIG. 2

Sept. 30, 1958 w. w. PHARIS 2,854,518

' DIGIT ADDING SELECTOR v Filed March 50, 1956 S Sheets-Sheet 5 l I l i 3n 111 J D |t-3o2 )J X X LEVEL MARKING TERMINALS 0 o o o O O O O O O O O O O O O O O O O O O O O O O 0 O O O I O O o o l o o o 0 Lo 0 TT RT ST HST FIG. 3

United States Patent DlGltT ADDENG SELECTOR William W. Pharis, Rochester, N. Y., assignor to General Dynamics Corporation, Rochester, N. Y., a corporation of Delaware Application March 30, 1956, Serial No. 575,261

4 Claims. (Cl. 179-18) My invention relates to telephone systems in general and more particularly to drop-back type selectors suitable for use in such telephone systems.

In step-by-step telephone systems, it has been the practice to provide multiple drop-back or digit adding type selectors which employed a plurality of level marking means, such as wipers cooperating with level indicating contacts. In some of these systems, such wipers are used in combination with other level marking means such as so-called normal post springs.

Accordingly, it is an object of my invention to provide a new and improved multiple drop-back digit adding type selector.

Another object of my invention is to provide a multiple drop-back type selector having simplified drop-back contact means which may be in the form of a single level marking wiper cooperating with a single set of level indicating contacts to achieve a drop-back type operation.

A feature of the selector forming the preferred embodiment of my invention is the provision of a set of relays operative in unique combinations for response to the order of sequence in which level marking terminals of the selector switch are energized for selectively controlling the switch releasing means, the means for initiating the hunting operation within a selected level, or the means for causing an advance of the wiper set of the switch to the overflow position.

My invention is employed in a two motion selector of the well known step-by-step type. The preferred embodiment of my invention includes a selector switch having a plurality of sets of terminals which are arranged in a plurality of levels and a set of wiper (brushes) having a normal position and operative through primary and secondary motions for extending connections to any of the sets of terminals. The advance of the wiper set in its primary direction is effective for causing the wiper set to select one of the levels. Thereafter, the wiper set is advanced in its secondary direction within the selected level. The switch also has means including a primary magnet operative in response to control signals for advancing the wiper set from its normal position in its primary direction. Subsequent to the selection of one of the levels, hunting means including a secondary magnet is effective for advancing the wiper set in its secondary direction into successive engagement with each of the sets of terminals within the selected level until an idle set of terminals is engaged by the wiper set. In the event that the wipers are driven within any one of the selected levels beyond the last set of terminals, means comprising a set of overflow contacts is operative for indicating the overflow condition and for rendering the hunting means inoperative. The switch is also provided with means including a release magnet for restoring the wiper set from an operated position in either the primary or secondary direction to the sets normal position.

In order to make the above-described selector switch carry out a multiple digit adding operation, i. e., succes- 'ice sively advance its wiper set in the primary direction and drop-back the wiper set to normal position upon the receipt of a first plurality of directive control signals of predetermined values, and to advance the wiper set to the overflow position upon the receipt of certain other directive control signals or combinations of signals, I provide a plurality of level marking terminals arranged in a set which may be selectively energized for indicating which of the levels has been selected by a primary advance of the wiper set. The selector switch also includes means including a level marking wiper operative in response to the operation of the primary magnet. Means comprising the level marking wiper is effective at the conclusion of the primary advance of the wiper set for selecting and energizing the one of the level marking terminals corresponding to the selected one of the levels. Means comprising a plurality of relays is operative in particular combinations in response to the order of sequence in which the level indicating terminals are energized for selectively controlling the release magnet, the means for causing the secondary magnet to advance the wipers into engagement Withthe first set of terminals in a selected level, or the means for causing the hunting means to advance the wiper set to the overflow position regardless of whether an idle one of the terminals sets is encountered.

Further objects and advantages of my invention will become apparent as the following description proceeds. The points of novelty which characterize my invention are set forth with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the description, reference may be had to the accompanying drawings in which:

Figs. l-3, when placed side by side in numerical order from left to right, show a telephone system including a digit adding selector and a skeletonized representation of a calling subscriber line.

The apparatus referred to in the following description is made to function from power supplied from a source such as a battery. The most positive terminal or plate of the battery is connected to ground and is referred to hereafter as ground and in the drawings as The most negative, ungrounded terminal or plate of the battery is referred to as battery and in the drawings as Seizing the selector Referring to Fig. 1, a connection may be extended from a calling station, such as A, to the selector shown in Figs. 1-3 over line 11 to which station A is connected and through line terminating circuit LC10, and other equipment such as a line finder (not shown). The aforesaid means for extending such a connection do not form a part of the presentinvention and therefore are not further described.

In response to the extension of a connection from station A to the selector a circuit for operating calling bridge relay is completed. The circuit may be traced as follows: from ground through break overflow contacts OF11, break contacts 211, the upper winding of relay 110, break contacts 104, conductors TC and 11a, control means such as dial contacts H11 at station A, conductors 11b and RC, break contacts 106, and the lower winding of relay 110 to battery.

The operation of relay 110 is effective for initiating the seizure of the selector by causing the operation of release delay relay 200. The circuit for operating relay 200 is completed from ground through make contacts 112 and the winding of relay 2% to battery. The operation of relay 200 is effective for sending back ground over the incoming sleeve conductor S, through break contacts 233, make contacts 206, break contacts MB12 of the make- 3 busy key to conductor S, and ultimately to line circuit LC10.

The operation of relay 110 is also effective for operating primary delay relay 210 by completing the following operating circuit: ground through make contacts 112, break primary off-normal contacts PON21, the upper winding of relay 210 to battery. The operation of relay 210 is effective for preparing an energizing circuit for the primary advancing means at make contacts 213. The operation of relay 210 is also effective for opening the above-described ground connection including overflow contacts OF11 to the upper winding of relay 110 at break contacts 211 and for substituting a grounded, low impedance tone source (not shown) which is in turn connected to the group dial tone conductor GDT through break contacts 312 and 302 and make contacts 212 to the right-hand terminal of the upper winding of relay 110. Owing to the make-before-break nature of contacts 211 and 212, the operation of relay 210 does not cause momentary interruption in the operating circuit of relay 110 so that relay 110 continues to be held in a steadily operated state during the time that relay 210 is operating. The connection of the group dial tone in series with the calling bridge relay 110 and the calling subscriber station A informs the subscriber at station A that the selector is in condition to receive directive impulses from the station dial.

Primary movement of the wipers The switch which is included in the preferred embodiment of the present invention is provided with a wiper set having brushes T, R, S, and HS which are mounted on a common carriage having a normal position and a plurality of main sets of terminals disposed for engagement by the wiper set. Each terminal within any set is arranged to be engaged by a corresponding one of the wipers in the wiper set. Thus each set has TT, RT, ST, and HST terminals. The sets of main terminals are arranged in a plurality of groups or levels such that the wiper set may be moved in a primary direction to a point that is opposite the first set of terminals within any one of the levels. Means comprising a primary magnet P20 is operative in response to directive signals transmitted from the calling station for selectively advancing the wiper set away from its normal position in its primary direction. The operation of the primary advancing means is described later in this description.

Level marking means comprising a plurality of auxiliary terminals such as the terminals generally designated XX is also provided. Each such XX terminal corresponds to one of the levels of main terminal sets. Means comprising an auxiliary wiper AW having a normal position is provided for energizing the one of the XX terminals corresponding to the level selected by the wiper set comprising brushes T, R, S, and HS. Wiper AW is arranged to be advanced one step away from its normal position for each primary step taken by the brushes T, R, S, and HS and to be restored to its normal position in response to the restoration of the wiper set comprising brushes T, R, S, and HS to its normal position.

In order to advance the wiper set to a desired level, a signal comprising a trainof one or more impulses is transmitted from calling station A to the selector. Each such impulse is caused by the momentary opening of contacts H11 of the dial at station A. Relay 110 is released in response to each impulse within a train of signals and reoperates after the impulse is terminated. Upon each release of relay 110 and in response to the operation of relays 200 and 210, a circuit is completed for energizing primary magnet P20. The circuit is traced as follows: from ground through break contacts 111, make contacts 203, 213 and 204, and magnet P20 to battery. An obvious holding circuit is also completed over substantially the same path for energizing the lower winding of relay 210 for purposes which are to be explained presently. Relay 200 is of the slow release type so that it is maintained in its operated condition during the time that relay 110 is in released condition during pulsing.

In response to the movement of the wiper set comprising T, R, S, and HS away from its normal position, the primary off-normal springs are operated so that the previously described seizure responsive operating circuit for relay 210 is opened at break primary off-normal contacts PON21. During the impulsing operation of relay 110, relay 210, a slow release type, is maintained in its operated condition owing to the intermittent energization of its lower winding in parallel with the magnet P over the previously mentioned holding circuit. At the conclusion of the transmission of a train of impulses, calling bridge relay comes to rest in its operated position thereby opening the holding circuit for relay 210 at break contacts 111. Relay 210 thereafter releases.

As previously mentioned, auxiliary wiper AW is advanced one step for each step taken by the wiper set comprising brushes T, R, S, and HS in its primary direction for the purpose of engaging the one of the XX level marking terminals corresponding to the level selected by the wiper set. At the conclusion of the primary advance of the wiper set, the release of primary delay relay 210 is effective for causing the wiper to energize the appropriate one of the level marking terminals. The circuit may be traced as follows: from ground through break contacts 233, make contacts 206, break contacts 102 and 215 to wiper AW and the selected level marking terminal.

Advance of the wipers in the secondary direction The selector which forms the preferred embodiment of my invention is adapted to be used as a conventional, single digit type selector as well as a multiple digit adding type. Assume for the moment that the level selected by the method described in the preceding section is one of the single digit levels. Such a level is characterized by M wiring connected to the corresponding level marking terminal. This is shown as the fifth level in the case being considered here. Operation of the selector following the selection of the fifth level is next described.

The selector is provided with means operative in response to the selection of a level such as the aforesaid fifth level effective for causing means comprising secondary magnet S20 and hunt assist relay 220 to advance the wiper set into engagement with the first set of terminals in the selected level. This level selection responsive means comprises a circuit for energizing relay 220; the energizing circuit is completed after a primary advance has been effected and before the wipers are advanced within the selected level. The circuit is traced from the fifth level marking terminal through M wiring, secondary off-normal break contacts SON21, break secondary interrupter contacts S21, the winding of hunt assist relay 320, break contacts 223 and release magnet contacts RL22 to battery. Relay 220 thereupon operates.

The operation of relay 220 is effective for completing a circuit for energizing secondary magnet S20. This circuit is traced from ground through break contacts 233, make contacts 206, break contacts 102, and make contacts 222, through magnet S20 to battery. The operation of relay 220 is also effective for completing a holding circuit for itself from ground through break contacts 233, make contacts 206, break contacts 102, make contacts 221, break contacts S21, the winding of relay 220, resistor R22, and break contacts RL22 to battery.

Energization of secondary magnet S20 at this time is effective for advancing the wiper set into engagement with the first set of main terminals within the selected level. The operation of the armature of the secondary magnet S20 is also-effective for opening the above-described holding circuit for relay 220 at secondary interrupter con- '5 facts S21. Relay 220 thereupon releases. The advance of the wiper set into engagement with the first and succeeding sets of terminals within the selected level is effective for operating secondary ofl-normal contacts SON21 thereby disconnecting the M conductor from its previously described connection to the winding of relay 220 at break contacts SON21. Thereafter further operation of relay 220 is dependent upon the energization of the busy test circuit which is next described.

Hunting for an idle set of terminals.The set of terminals engaged by the wiper set is next tested to determine whether or not the set is in busy or idle condition. In the selector forming the preferred embodiment of my invention a busy condition on any set of terminals to which the wiper set has access is indicated by the presence of ground on the corresponding one of the ST terminals. An idle condition is indicated by the absence of such ground. In the event that the test indicates the currently engaged terminal set is busy, the secondary advancing means comprising relay 220 is energized by means comprising a busy test circuit in order to advance the wiper set into engagement with the next succeeding terminal set in a hunting operation. This hunting operation is repeated until an idle terminal set is located or until the wiper set has been advanced to the overflow position.

Assuming that the first terminal engaged by the set of wipers is busy, a ground signal on the ST terminal transmitted over the busy test circuit, comprising wiper S, break contacts 108, make contacts 207, and break contacts OFZl and S21 to the winding of relay 220 is effective for operating relay 220 which in turn reenergizes magnet S20 and reestablishes the above-described locking circuit for relay 220. Magnet S20 thereafter operates in the previously described manner to advance the wiper set into engagement with the next succeeding set of terminals within the selected level. Relay 220 thereafter releases in the previously described manner in order to allow the busy test of the engaged terminal set to be repeated.

The operation of the secondary off-normal springs when the wiper set is moved in the secondary direction into engagement with the first set of terminals in a selected level is also efiective for thereafter extending ground to the operating circuit of the switchthrough relay 100. This circuit is traced as follows: from ground through break contacts 233, make contacts 206 and make contacts SON11 to the right hand terminal of the winding of relay 100. During the time that a busy signal is transmitted over the busy test circuit, the ground signal so transmitted is extended over an obvious connection to the left-hand terminal of relay 100 thereby shorting out relay 100 so that the relay is not operated during the time a busy terminal set is engaged by the wiper set.

Seizure of an idle set of terminals.When the wiper set comprising brushes T, R, S, and HS has been advanced in the secondary direction into engagement with a main terminal set which is in idle condition, i. e., no busy-indicating ground signal is connected to the abovetraced busy test circuit, the short around the winding of switch-through relay 100 is removed by the absence of busy-indicating ground on the left-hand terminal of relay 100. Relay 100 then operates in series with the windings of relay 220. This circuit is traced as follows: from the above traced ground supply to the right hand terminal of the winding of relay 100, through the winding of relay 100 and break contacts OF21 and S21, the winding of relay 220, and break contacts 223 and RL22 to battery. The combined resistance of the windings of relays 100 and 220 has a value to allow current flow sufiicient to operate relay 1'00 but insufficient to operate relay 220. Consequently only relay 220 is not operated at this time.

The operation of relay 100 is effective for transferring the brush S from its connection to the above-traced busy test circuit at contacts 108 to a connection to the incoming sleeve conductor SC at contacts 107., Ground subsequently passes back from the succeeding apparatus connected to the ST terminal of the selected set in the well-known manner is effective for supplying ground to the right-hand terminal of the relay to the preceding sleeve conductors. This circuit is traced as follows: from brush S, through make contacts 107, break contacts MB12, to the incoming sleeve conductor S. The operation of relay 100 is also effective for transferring the incoming TC and RC conductors to which the calling station A is connected from the above traced connection to the windings of relay at contacts 104 and 106, respectively, to a connection through the succeeding equipment connected to conductors connected to the TT and TR terminals of the selected set by way of brushes T and R at make contacts 103 and 105, respectively. The extension of a metallic connection from calling subscriber station A to the succeeding equipment is effective in the well-known manner for causing the calling subscriber station to seize the succeeding apparatus. The operation of relay 100 is also effective for transferring the incoming HSC conductor from its normal connection through break contacts OF13 and resistor R11 to ground at break contacts 109a to a metallic connection With the conductor connected to the selected one of the HST terminals selected by the operation of the wiper set at make contacts 109. The operation of relay 100 is effective for disconnecting the energizing ground from auxiliary wiper AW at breakcontacts 102 so that the wiper is no longer effective for energizing the level marking terminal corresponding to the selected level.

The above-described transfer of the calling station from the connection to the windings of relay 110 is effective for causing the latter relay to release. The release of relay 110 is effective for opening the previously described energizing circuit for relay 200 which thereafter releases. The selector circuit is maintained in this condition until an on-hook condition is indicated by the removal of ground from the sleeve conductor of the succeeding circuit.

Release of the selector to its normal condition-Release of a connection established through the selector and the succeeding equipment is indicated by the removal of ground from the ST terminal of the selector terminal set by means well understood by those skilled in the telephone art. Upon the removal of ground from brush S, the above-traced locking circuit for relay 100 is opened thereby releasing relay 100. The release of relays 100 and 200 is effective for closing an energizing circuit for means comprising release magnet RL10 for restoring the wiper set as well as the wiper AW to their normal positions. The energizing circuit is traced from ground through break contacts 201 and 101, through now closed make contacts PONll and SON11 in parallel, and the winding of magnet RL10 to the battery. The release of relay 100 is also effective for reestablishing the above-traced connection from incoming conductors TC and RC to the windings of relay 110 at break contacts 104 and 106, the connection of incoming conductor HSC to the normal resistance ground at contacts 109a and the incoming sleeve conductor to the selector ground supply circuit at break contacts 102. The circuit is now in normal condition and ready for further use.

The digit adding process While the subject selector is adapted for use on particular levels, such as the fifth, which are characterized by M wiring connected to the level marking terminal for single digit operation, the selector is also adapted to absorb one or more particular digits before advancing in the secondary direction. It is this multiple digit adding process which is next described.

In order to adapt a selector such as the one forming the preferred embodiment of the present invention to meet the requirements of the system in which it is in- 7 corporated, it may be necessary to provide means for absorbing or adding one or more preliminary signals transmitted from a calling station. This adding process is accomplished by advancing the selector switch in its primary direction as many times as there are signals to be added and providing means effective at the conclusion of each such primary advance for operating the restoring means. Thus the selector switch is dropped back until the first signal which is to be used to direct the selector in the switching process is received. When the latter event takes place, the brushes T, S, R, and HS of the selector are advanced within the selected level in substantially the same manner as the one previously described.

In the selector forming the preferred embodiment of my invention, the digit adding or drop-back operation is achieved by including in the selector means comprising digit register 1 and digit register 2, relays, 300 and 310, respectively. These relays are selectively operative in unique combinations in response to the energization of certain ones of the level marking terminals when energized in a particular order of sequence for extending connections from the level marking terminals to the previously described restoring means, and the means for causing the secondary magnet to advance the wipers into engagement with the first set of terminals in a selected level and for causing the busy test means comprising the busy test circuit to advance the wipers within a selected level to the overflow position.

Three or more digit adding.Signals which are to be added when dialed as a first digit are effective for directing auxiliary wiper AW in the previously described manner to the level marking auxiliary XX terminal to which NV wiring is connected. In the example chosen, the NV" wiring is connected to the ninth terminal. At the conclusion of the transmission of the signals, release of primary delay relay 210 is effective for extending ground to auxiliary wiper AW to energize the ninth terminal in the previously described manner. The energization of the ninth terminal is eifective for causing a first selective operation of means comprising digit register relays 300 and 310 by extending ground over NV wiring to the winding of digit register 1 relay 300. The circuit is traced from NV wiring through break contacts 313, the upper winding of relay 300, and break contacts RL22 to battery.

The first selective operation of relays 300 and 310 (i. e., with relay 300 operated and relay 310 unoperated) is effective for energizing the restoring release magnet RL10. The magnet energizing circuit is traced from NV wiring through break contacts 313, make contacts 305 and 202, break contacts 101, now operated primary off-normal make contacts PON11 and the winding of the release magnet to battery. Magnet RLIO thereupon operates, restoring AW to deenergize the ninth XX terminal and the set comprising wipers T, R, S, and HS to their normal positions. The restoration of the wipers is etfective for restoring the operated primary off-normal springs thereby reclosing the above-traced operating circuit for primary delay relay 210 at contacts PON21. The resulting reoperation of relay 210 is eifective for deenergizing the level marking terminal by opening the above-traced ground path to auxiliary wiper AW at break contacts 215.

The operation of relay 300 is effective for closing a temporary locking circuit for itself which is traced from ground through break contacts 233, make contacts 206, break contacts 102, break contacts 3192, make contacts 309a and the lower winding of relay 300 to battery. As a result of the establishment of this locking circuit, the above-described deenergization'of the ninth level marking XX terminal is not effective for releasing relay 300 at this time. Also in response to the operation of relay 300, the previously traced circuit for connecting dial tone to the calling subscriber station is opened at break 8 contacts 302. Direct ground is substituted for the low impedance dial tone connection by the closing of make contacts 301. As a result, the calling subscriber station A is not given a dial tone signal following the transmission of the first added digit signal.

Following the transmission of the first signal to be added and the first selective operation of the digit registering means in the above-described manner, an indefinite number of intermediate signals or digits characterized by the advance of wiper AW to XX terminal levels to which either NV or N are connected may also be absorbed without altering the condition of the selectively operated means. Thus, following the operation of relay 300 in response to the transmission of the first signal to be absorbed, the subsequent transmission of a second signal of the same value is etfective for moving wiper AW to the ninth level and reenergizing the NV conductor thereby again extending ground for operating the release magnet RL10 over the previously traced circuit through contacts 305. Similarly, if the intermediate signals include one of the value to advance wiper AW to an XX terminal to which N wiring is connected (the sixth terminal in the case considered here) an obvious circuit for energizing release magnet RLIO is also completed through make contacts 309 on now operated relay 300. The operation of release magnet RL10 is etfective in the previously described manner to restore the wipers to their normal positions thereby reoperating primary delay relay 210 and thereby removing the energizing ground from auxiliary wiper AW by opening break contacts 215.

The final (unlocking) signal of the group of signals to be absorbed by the selector is effective for advancing auxiliary wiper to the level marking XX terminal to which Z wiring is connected. In the case chosen for discussion here, Z wiring is connected to the eighth level. At the conclusion of the transmission of the signal the energization of the eighth XX terminal in the previously described manner occurring after the operation of relay 300 is eifective for causing another selective operation of the digit registering means in order to prepare a circuit for energizing the means for advancing the wiper set into engagement with the first set of terminals in the level selected. Thus, the energization of the Z wiring is effective for operating relay 310 over the following circuit: from Z wiring through make contacts 307, break contacts 31%, the winding of relay 310, break contacts 319 and RL22 to battery. The operation of relay 310 is effective for establishing a locking circuit for itself from battery through make contacts 319a, the winding of relay 310, make contacts 319e, break contacts 102, make contacts 206, and break contacts 233 to ground. The operation of relay 310 is also etfective for substituting a locking circuit for relay 300 which is traced through make contacts 319f, break contacts 215 and 102, make contacts 206, and break contacts 233 to ground for the previously traced locking circuit through break contacts 3192. Thus relay 300 is held in its operated condition only so long as the substitute holding circuit is closed at contacts 215 owing to the released condition of relay 210. The operation of relays 300 and 310 and the energization of the eighth XX terminal are effective for operating the release magnet RL40 by extending ground over the Z conductor through make contacts 307, 319d and 202, break contacts 101, and primary off-normal make contacts PON11 to the winding of magnet RL10 and battery. The energization of magnet RL10 is effective in the previously described manner to restore the wiper set to normal condition as well as reoperate relay 210. The reoperation of relay 210 is effective for opening the above-traced substitute locking path of relay 300 at break contacts 215. Relay 300 releases at this time and thereby places the selectively operated means comprising relays 300 and 310 in still another condition, namely, 300 released and 310 operated.

Following the subsequent transmission of a signal from calling station A which is eflective for causing wiper AW to -energize level marking terminals characterized by NV, N, Z, RW, M, or VZ Wiring the Se lectively operated means'including relays 300 and 310 is effective for rendering operative the previously described circuit means including conductor M for advancing the wiper set comprising brushes T, R, S, and HS into engagement with the first set of main terminals within the level so selected. Thus, the energization of the ninth terminal (NV wiring) is effective for interconnecting NV wiring and conductor M at make contacts 314. Similarly, energization of any one of the sixth, seventh, or fourth auxiliary XX terminals is efiective at this time for extending ground to the M conductor to 220 by way of break contacts 308 and make contacts 316; make contacts 316; and break contacts 309a and make contacts 318; respectively. The energization of the M conductor is effective in the previously described manner for energizing relay 220 in order to initiate the secondary movement of the wiper set in the previously described manner. Thereafter the wiper set is advanced within the selected level until an idle terminal set is located or until the set has been advanced to the overflow position.

Single digit adding.-In the event that it is desirable to have the selectively operated means comprising relay 300 and 310 prepared in response to the transmission of a single unlocking signal from a calling station for energizing the previously described circuit means which is effective to advance the wipers into engagement with the first main terminal set in a subsequently selected level, means comprising the VZ wiring shown in the preferred embodiment of my invention connected to the fourth level marking XX terminal is provided. In the event that the first signal transmitted to the selector circuit is effective for advancing wiper AW into engagement with the fourth XX terminal, the subsequent energization of such terminal is effective for causing both relays 300 and 310 to be operated. Following the transmission of the signal and the energizing of the fourth XX terminal in the previously described manner, relay 300 operates over the following circuit: from ground placed on wire VZ through break contacts 309a and 317, the upper winding of relay 3%, and break contacts RL22 to battery. The preliminary make nature of contacts 3090 insures that the operation of relay 300 is effective for establishing a locking circuit from ground supplied through break contacts 233, make contacts 206, break contacts 102 and 319e, make contacts 3090 and the lower winding of relay 300 to battery prior to the opening of the abovetraced operating circuit in response to the operation of relay 300 at break contacts 309a. Upon the operation of relay 300, an operating circuit for relay 310 is completed. The circuit is traced on the VZ wire, through make contacts 30%, break contacts 319d, the winding of relay 310, break contacts 319 and RL22 to battery. The operation of relay 310 is effective for establishing the above-described substitute locking circuit comprising make contacts 319 for relay 300.

The operation of relays 300 and 310 is eifective for completing the above-traced energizing circuit for release magnet RL from conductor VZ, through make contacts 309b, 319d and 202, break contacts 101, make contacts PONll and the winding of magnet RL10 to battery. Release magnet RL10 thereupon operates and is eflective in the previously described manner for restoring both the wiper set comprising wipers T, R, S, and HS and wiper AW to their normal positions. In the previously described manner, the restoration of the wiper set to its normal condition is effective for restoring the primary off-normal contacts thereby recompleting the seizure responsive operating circuit for relay 210.

The operation of relay 210 is effective, by opening break contacts 215, to remove the energizing ground from the substitute locking circuit, including contacts 319 of relay 300 so that relay 300 is restored to its normal position at this time. With relay 300 in its normal condition and relay 310 operated, the selectively operated means comprising relays 300 and 310 has prepared the previously described circuit means for extending a connection from the fourth level marking terminal to the winding of hunt assist relay 220. Upon the transmission of a subsequent directive signal to the selector, relay 220 is energized over this circuit and is effective in the previously described manner to cause the wiper set comprising T, R, S, and HS to be advanced into engagement with the first terminal set in the selected level. Thereafter the secondary advancing means which includes relay 220 and magnet S20 is effective in the previously described manner to initiate a hunting operation within the level selected.

Hunting t0 0verfl0w.The selectively operated means comprising relays 300 and 310 is also effective for preparing means comprising a circuit for connecting certain ones of the level marking XX terminals to the abovedescribed busy test circuit, so that a busy condition is simulated on each of the main sets of terminals engaged by the wiper set. Thus the wiper set comprising brushes T, R, S, and HS is advanced within a selected level to the overflow position regardless of the busy or idle condition of the main terminal sets encountered during the advance after the level has been selected. Thus, in the event that the auxiliary wiper is used to energize the levels characterized by Q (tenth level), RW (seventh level) wiring on the corresponding level marking XX terminals prior to the transmission of a signal effective for operating relay 300 or 310, a connection is completed through either break contacts 303 or break contacts 315 on relays 300 and 310, respectively, to the conductor extending to the sleeve wiper. The energization of the tenth or seventh level marking terminals at the conclusion of the transmission of such a signal by the closing of contacts 215 is thereafter eflective for placing ground on the previously traced busy test circuit so that hunt assist relay 220 and secondary magnet 820 are operated in the previously described manner to advance the wiper set within the tenth or seventh levels into overflow position, i. e., a point beyond the last set of terminals within the selected level.

The switch includes the means comprising overflow contacts operative in response to the advance of the wipers to the overflow position for connecting busy tone to the calling subscriber line to inform the subscriber that a connection cannot be so established. The circuit is traced as follows: from the busy tone source through conductor BT, make overflow contacts CF12, break contacts 211, thence through the calling subscriber loop through the windings of relay over the previously traced circuit. The operation of the overflow contacts is also effective for disabling the secondary advancing circuit by opening the previously traced busy test circuit extending from sleeve wiper S to the winding of relay 220 at break contacts CF21 thereby preventing the further operation of relay 220 and magnet S26.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects. I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What is claimed is:

. 1. In a digit adding selector comprising a plurality of sets of main terminals disposed in a plurality of levels and a switch including a set of wipers having a normal position, said wipers being operative in a primary direction for selecting one of said plurality of levels and thereafter operative in a secondary direction within a selected one of said levels for extending a connection from said selector to one of said main terminal sets within the selected one of said levels, means responsive to control 11 signals for advancing said wiper set in its primary direction, means for advancing said wiper set in its secondary direction within a selected one of said levels, means for causing said secondary advancing means to advance said wiper set into engagement with the first of said main sets of terminals in a selected one of said levels, means operative in response to a busy condition on a main set of terminals engaged by said wiper set for causing said secondary advancing means to advance said Wiper set into engagement with the next succeeding one of said main terminal sets in a selected one of said levels, means operative in response to the secondary advance of said wiper set beyond the last of said main terminal sets for indicating an overflow condition, and means for restoring said wiper set to its normal position; the combination comprising a plurality of auxiliary terminals for indicating the selected one of said levels; means comprising a single wiper operative in response to the operation of said primary advancing means for energizing the one of said auxiliary terminals corresponding to the selected one of said levels; and means operative in response to the sequential energization of certain ones of said level indicating auxiliary terminals for selectively operating said wiper restoring means, said means for causing said secondary advancing means to advance said wiper set into engagement with the first of said terminal sets, and said busy test means.

2. The selector set forth in claim 1 wherein said selectively operable means operated in first, second, and third manners is efiective for completing energizing circuits from certain ones of said auxiliary terminals to said restoring means, said means for advancing said wipers into engagement with the first of said main terminal sets in a selected one of said levels and said busy test means respectively.

3. The selector set forth in claim 1 wherein the selective means is operative to any one of a plurality of conditions and the energizations of certain ones of said auxiliary terminals in response to the operation of said selective means to certain ones of said conditions is effective for operating corresponding ones of said restoring means, said means for advancing said wipers into engagement with the first of said main terminal sets in a selected one of said levels, and said busy test means.

4. The selector set forth in claim 1 wherein said selectively operated means comprises a plurality of contact bearing relays, means comprising certain of said auxiliary terminals for operating said relays in various combinations, means comprising certain of said contacts being eifective in response to certain operated combinations of said relays for extending energizing circuits from certain of said auxiliary terminals to said restoring means, said means for advancing said wipers set into engagement with the first of said main terminal sets in a selected one of said levels, and said busy test means.

No references cited. 

